Device and method for degassing solvent-containing polycarbonate solutions

Abstract

The invention relates to an apparatus and a process for devolatilizing solvent-containing polycarbonate solutions. By employing the inventive apparatus, polycarbonates with low residual values of volatile constituents are produced from solvent-containing polymer melts, which improved optical properties, especially yellowness index, with the aid of an apparatus combination of a heatable tubular devolatilizer and a vented extruder.

1. An apparatus for devolatilizing solvent-containing polycarbonate melts, the apparatus comprising:
 a downpipe devolatilizer combined with 
 a vented extruder, said downpipe devolatilizer being arranged directly above said extruder. 
 
     
     
       2. The apparatus as claimed in  claim 1 , further comprising vapor lines mounted on the downpipe devolatilizer. 
     
     
       3. The apparatus as claimed in  claim 1 , wherein the downpipe devolatilizer includes a shell-and-tube heat exchanger having a plurality of pipes which are heated from the outside. 
     
     
       4. The apparatus as claimed in  claim 1 , wherein the downpipe devolatilizer is heated by means of condensing steam, by means of a condensing organic heat carrier or by means of a liquid organic heat carrier. 
     
     
       5. The apparatus as claimed in  claim 1 , wherein the combination of the downpipe devolatilizer and the vented extruder is upstream of at least one further downpipe devolatilizer. 
     
     
       6. The apparatus as claimed in  claim 1 , wherein the vented extruder is of two- or four-shaft design. 
     
     
       7. The apparatus as claimed in  claim 1 , wherein the vented extruder comprises a closely intermeshing, corotatory twin-screw extruder. 
     
     
       8. The apparatus as claimed in  claim 1 , wherein the extruder comprises a plurality of devolatilizing zones in a conveying direction. 
     
     
       9. A process for devolatilizing polycarbonate solutions as claimed in  claim 1 , the process comprising:
 preparing a polycarbonate solution comprising at least one organic solvent and at least one polycarbonate by the interfacial process; and 
 supplying the prepared polycarbonate solution to a downpipe devolatilizer in combination with a vented extruder, said downpipe devolatilizer being arranged directly above the extruder such that the polymer solution falls directly into the vented extruder. 
 
     
     
       10. The process as claimed in  claim 9 , further comprising removing solvent-containing vapors, formed in the downpipe devolatilizer, directly from the housing of the flash devolatilizer by means of vapor lines. 
     
     
       11. The process as claimed in  claim 9 , further comprising injecting inert gases as entraining agents into and mixed into a polymer melt stream upstream of the downpipe devolatilizer. 
     
     
       12. The process as claimed in  claim 11 , wherein the inert gas is injected as entraining agent in one or more housings of the vented extruder. 
     
     
       13. The process as claimed in  claim 9 , wherein the input concentration of the polycarbonate into the downpipe devolatilizer is between 60% by weight and 95% by weight. 
     
     
       14. The process as claimed in  claim 9 , wherein the polycarbonates obtained have a residual solvent content of 20 ppm to 1000 ppm.